When a blood clot that has formed in a vein of the lower part of the body breaks loose and migrates to the lungs, pulmonary embolism results. These clots obstruct the flow of blood through the lungs and interfere with the normal oxygenation of the blood. Whereas small clots may be tolerated and eventually reabsorbed, large clots (greater than three millimeters in diameter and up to 30 centimeters in length) can cause shock or sudden death. Pulmonary embolism causes approximately 200,000 deaths in the U.S.A. each year.
Pulmonary embolism has a tendency to recur. If a patient has had one pulmonary embolism, there is a probability of about 70% that he will have another. If the patient survives the initial embolism, treatment is usually directed toward preventing further blood clot formation in the veins (anticoagulation). However, some patients cannot be given anticoagulants, for example after injury, surgery or stroke, and others may have recurrent embolism despite anticoagulant treatment. Further, anticoagulants do not affect clots already formed.
As an alternative to anticoagulants, the travelling clots (emboli) may be prevented from reaching the lungs by interrupting their passage through the inferior vena cava, the great vein which returns blood from the lower half of the body to the heart and lungs. Traditionally this has been done by direct surgery on the vena cava; the vena cava has been simply tied (ligated), or its cross-section has been subdivided by a variety of sutures or clips. More recently the vena cava has been interrupted by inserting into the vena cava a filtering or obstructing device indirectly via a remote but more accessible vein, such as the jugular vein in the neck or the femoral vein in the groin.
There are known in the prior art several devices to interrupt the travel of emboli. All of these devices require surgical dissection of the vein of entry for their insertion.
First, the Miles or Adams-DeWeese plastic clip may be used to flatten and subdivide the lumen of the vena cava from the outside. This is very effective in interrupting the travel of emboli. However, this device requires major abdominal surgery, sometimes on very sick patients. There may be complications of the abdominal surgery or the general anesthesia even though the clip itself is effective and is not subject to local complications such as bleeding, perforation or migration.
Alternatively, several prior art transvenous devices are known. The most popular devices are the Mobin-Uddin umbrella, the Kimray-Greenfield filter, and the Hunter balloon.
All three require surgical dissection of the internal jugular vein in the neck or the femoral vein in the groin, usually under local anesthesia. The vein must be opened to insert the capsule containing the folded device or the collapsed Hunter balloon. This dissection may take half an hour to three hours before the folded device or collapsed balloon can be inserted into the large vein. The procedure is very uncomfortable for the patient who must lie still during the dissection.
The dissection is usually done by a surgical team consisting of a surgeon, an assistant and an operating room nurse in addition to the radiologist and radiologic technologist. A delay of some hours is usually required to mobilize this team. The radiologist generally prechecks the anatomy of the vena cava fluoroscopically by injecting contrast agent through a catheter positioned near its lower end. He guides the device into optimal position for delivery. The umbrella, filter or inflated balloon is released into the vena cava. The radiologist may inject contrast medium after delivery in order to check for position and/or patency of the device.
Dissection of the vein is associated with a risk of local hemorrhage and a further risk of air embolism through the vein incision. Further, the device may be difficult or impossible to insert, and it may prove difficult to steer the device into its correct position. The insertion process is thus complex, time consuming, expensive and sometimes associated with surgical complications at the site of introduction. Generally the large vein in the neck or groin is sacrificed after removing the delivery system.
In addition there are problems associated with specific devices.
The Mobin-Uddin umbrella (described in U.S. Pat. No. 3,540,431, issued Nov. 17, 1970) may be dislodged and migrate toward the heart and lungs. The device tends to become totally obstructed by even small amounts of embolus. Elevated venous pressure occurs below the umbrella, and this may cause leg edema. Thrombosis may occur in the cul-de-sac above the umbrella and this can be a source of recurrent pulmonary emboli. Finally, perforation of the vena cava wall with local hemorrhage may occur.
The Kimray-Greenfield filter is described in U.S. Pat. No. 3,952,747, issued Apr. 27, 1976. Using the Kimray-Greenfield filter, there may be difficulty inserting the capsule, which is relatively large. The device tends to tilt backward or sideways during or after delivery, becoming mechanically less effective. The device may migrate distally due to the waterhammer effect of the column of blood above the filter. Perforation of the vena cava may occur, sometimes with local hemorrhage. Moderate sized emboli may pass through the filter, particularly if it is tilted or the vena cava is large. However, proximal migration of the Kimray-Greenfield filter has not been reported, and the device generally remains clot free.
The Hunter balloon device is designed to completely occlude the lumen of the vena cava, and thus may cause leg edema. Large collateral veins open up and these may also allow passage of dangerous emboli. This device is also expensive. However, the Hunter balloon has the advantage that it can be repositioned, if necessary, before release. It is not associated with perforation or local hemorrhage and migration is rare.
In view of the problems with these prior art devices, it would be desirable to provide a device for preventing pulmonary embolism that can be inserted into the vena cava without surgical dissection of a vein of entry. It is further desirable to provide such a device that can be inserted immediately upon diagnosis of the need for the device, at the time of the diagnostic procedure, without calling upon a surgical team.
It is also desirable to provide such a device that is easy to insert, takes very little time to insert, and is associated with minimal risk of surgical complications such as local hemorrhage or air embolism.
It is further desirable to provide means for inserting the device which is easy to use and is adapted for use with existing apparatus used during the diagnostic procedure.
It is therefore an object of the invention to provide a filter for interrupting the travel of emboli that can be inserted by the radiologist at the time of diagnosis, without requiring the presence of a surgical team.
It is also an object of the invention to provide such a filter that can be firmly attached to the vein, that is not easily dislodged, that does not tend to become totally obstructed by retained emboli, that does not tend to cause thrombosis, leg edema or other complications, and that retains all potentially dangerous emboli.
It is an additional object of the invention to provide means for inserting such a filter into the patient that is easy to use, and is adaptable for use with standard angiographic catheters used during diagnostic procedures.
Commonly, for procedures involving placement of a catheter in a blood vessel of a patient, a needle is first inserted in the blood vessel; a guide wire is then threaded through the needle; the needle is then withdrawn over the guide wire; and finally the catheter (tubing) is inserted into the vessel over the guide wire. This method is known as the Seldinger technique. The insertion of the guide wire requires skill, and a problem ofter occurs when the wire meets resistance and buckles (outside the patient), after which the wire cannot be used and must be withdrawn, and another wire started. It would be desirable to provide a guide wire feed device which will prevent this problem. The device according to the present invention can be used to deliver any guide wire. In particular, it is used to deliver a guide wire which in turn delivers the filter of the invention through the catheter, as described herein.